phranque - 8:36 am on Mar 11, 2013 (gmt 0)
the "choice made by (google)" was to "not provide" keyword search terms for visitors using secure protocol to search. (for example searching while "logged in to google")
the number of searchers using secure protocol has increased steadily since google implemented this policy in october, 2011.
i believe the reference to mobile search implies that these visitors are typically logged in while searching from mobile devices.